Chen Yuanhua

Research of capacitor voltage balance control method for H-bridge inverter of hybrid 9-level inverter

This paper proposes a capacitor voltage balance control method for low-voltage H-bridge inverter of hybrid 9-level inverter based on capacitor voltage imbalance predictive estimation and the injection of zero-sequence voltage. To investigate the proposed method, the charging model of capacitor voltage of H-bridge inverter is established and the inherent mechanism of capacitor voltage imbalance is analyzed in detail. The principle of the proposed method is simple to implement without additional hardware equipment. The simulation and experimental results demonstrate the validity of the proposed method.

Research on 35kV Cascaded Statcom and ITS application

A Cascaded transformerless Static Synchronous Compensator (STATCOM) of 35kV/8Mvar has been successfully developed and putted into application. The STATCOM is self-excited and in star configuration, each phase consists of twenty-one units, which employees 3.3kV IGBTs. With power supply by itself and the adjacent one, each unit can be bypassed and thus implement N-1 redundant running. By optimized Carrier Phase-Shift PWM method, the frequency of STATCOM can be dropped as low as 275Hz with the efficiency as high as 99%. Based on high speed distributed digital processors and instant current control method, the device has realized synthesized voltage and reactive power regulation and VQC/AVC coordination. The response time of STATCOM is below 10ms when voltage sag detected, thus strongly sustain the power system voltage. The experimental data and the field operation results both show that the performances of the developed transformerless 35kV/8Mvar STATCOM are satisfied, which provides a new solution for voltage and reactive power control for electric power substation.

Three level high voltage VSI adjustable speed IM drive system with IGCTS

In this paper, a three level high voltage VSI (voltage source inverter) adjustable speed IM (induction motor) drive system with IGCTs (integrated gate commutated thyristors) is developed. Two IGCTs are in series connection in each cell of the inverter in order to obtain a 6 kV high voltage output. The DSP (data signal processor) with FPGA (field programming gate array) controller is adopted to fulfill an optimized constant V/Hz control strategy. SHE-PWM (selective harmonic eliminated)-(pulse width modulation) method is carried out to keep sine wave output.